1. Field of the Invention
The present invention relates to a drive control circuit, an emission control circuit utilizing the drive control circuit, a communication apparatus provided with the emission control circuit and a drive control method, and it particularly relates to a technology by which to drive and control a load using the pulse-width modulation.
2. Description of the Related Art
Battery-driven type mobile devices, such as cellular phones or PDAs (Personal Digital Assistants) use LED (Light-Emitting Diode) devices for various purposes, such as a backlight of an LCD (Liquid Crystal Display), a flash for an attached CCD (Charge-coupled device) camera or blinking of LED elements with different emission colors. Reference (1) in the following Related Art List, for instance, discloses a system in which various colors are emitted by mixing blue, green and red emitted by their respective LED elements. Since the emission of light by LED elements is carried out by a pulse-width modulation (PWM) scheme, the three LED elements are connected to their respective PWM circuits via three output-stage transistors.
The drain, source and gate of an output-stage transistor are coupled to the cathode, reference voltage and PWM circuit of an LED element, respectively. And the LED element will emit light when a pulse signal outputted from the PWM circuit goes high and the output-stage transistor turns on. The longer the period in which the pulse signal is high, the more the light emission amount of the LED element will be. On the other hand, the emission of various other color lights than blue, green and red is accomplished by varying the light emission amounts of the LED elements through control of the respective duty ratios of the pulse signals to be outputted from the three PWM circuits.